1. Field
The following description relates to an electric motor that is used for converting electrical energy into mechanical energy in a variety of fields, such as electric vehicles, home appliances, and the like.
2. Description of the Related Art
Electric vehicles using an electric motor as a power source have gained more popularity due to harmful environmental effects from air pollution and the depletion of fossil fuels. Electric vehicles are may be classified as pure electric vehicles and hybrid electric vehicles. Pure electric vehicles are vehicles that use only an electric motor as a main power source. Hybrid electric vehicles are vehicles that use an internal combustion engine as a main power source, and an electric motor as an auxiliary power source. Electric vehicles are designed for the purposes of high torque at a low speed, high-speed operation, lightweight, etc. In order to achieve these purposes, power density of an electric motor, adopted in electric vehicles, is considered to be important. Electric vehicles may have an in-wheel system. The in-wheel system is a system in which an electric motor is mounted in an inner space of the wheel, so as to directly transmit power of the electric motor to the wheel.
In the in-wheel system, a brake, a bearing for supporting a hub, etc., are installed in the inner space of the wheel, and the electric motor is mounted in the remaining inner space. Accordingly, the electric motor needs to have a structure for improving output density, and a thin structure for having a short axial length, in order to avoid interference with a vehicle body.
The electric motor is also used in other applications, such as home appliances, etc. For example, a direct drive washing machine may have a structure in which an electric motor is connected to a tub. In order to minimize a space of the tub which protrudes backward due to the electric motor in the washing machine, the electric motor needs to have a thin structure for having a short axial length. In addition, since the washing machine needs a high torque at a low speed, high-speed operation, etc., output density of the electric motor, adopted in the washing machine, needs to be improved.